1) Field of the Invention
This invention relates to a connecting system for a line tube, which can be pivoted about a rotation axis, of a solar-thermal installation.
2) Description of the Prior Art
For an environmentally friendly energy generation, solar-thermal power plants are used now to an increasing extent. Such power plants usually include solar collectors, such as parabolic mirrors. With these solar collectors the solar radiation is collected and via receiver tubes or absorber tubes released into a carrier fluid, e.g. thermal oil. Via these absorber tubes and line tubes connected therewith the carrier fluid richer in energy then is transported. Inside the system or the line tubes, temperatures of 500° C. or more can be reached.
Since the solar collectors must be designed to be movable due to the apparent movement of the sun, the line tubes conveying the hot and pressurized carrier fluid often must also be pivotable. They are, however, always connected with stationary lines for passing on the carrier fluid. Due to the high temperatures and the high pressures, high demands consequently are placed on the connection between the individual parts of a solar-thermal installation.
The German Patent Application 10 2007 048 745 for example proposes an apparatus by means of which a perfect movability of the solar collectors is ensured at high temperatures and/or pressures. A flexible tube connection is arranged between a fixed line and an absorber tube, and there is provided a means for connecting the flexible tube line with the absorber tube with zero torque and/or zero force.
While the installations operated with thermal oil have so far been limited to a maximum operating temperature of 400° C. and a maximum operating pressure of 40 bar, novel solar-thermal installations are designed for operation with steam at 500° C. and at an operating pressure of 120 bar, in order to increase the effectiveness and the process efficiency.
Because of this extreme pressure load at a very high temperature and the involved risks and the high wear, other fluids or gases are considered as carrier fluid.
For example, there can also be used gases or liquefied salts which provide for transportation of the solar heat from an absorber tube to the power plant at temperatures of 500° C.
The increase in temperature to 500° C., however, causes a distinctly higher longitudinal expansion both of the line tubes of a solar-thermal installation and especially of the absorber tubes heated by the solar collectors and also of the tube lines in the fixed network. In addition, a more resistant seal must be used in operation with liquid salts. As a result, the previously employed flexible connections reach their application limits in the commonly used arrangement.